The invention relates to synaptic receptors that mediate transmission in the peripheral and central nervous systems. In particular, the invention concerns a new human 5-HT3 receptor that expands the repertoire of targets for pharmaceutical compounds.
Synaptic transmission in the peripheral and central nervous systems is regulated by a multiplicity of ligand-gated ion channels. This superfamily of receptors includes the xcex3-amino butyric acid (GABA) receptor, the glycine receptor, and the acetyl choline receptor, as well as receptors responsive to serotonin (5-HT). The GABA-, glycine-, and acetylcholine-gated receptors are formed from mixtures of homologous subunits in various combinations. Serotonin-gated receptors fall into at least three subclasses. 5-HT1 and 5-HT2 receptors are described in U.S. Pat. No. 5,155,218. The 5-HT1 and 5-HT2 receptors are characterized by seven transmembrane regions; however, the 5-HT3 receptors are ligand-gated ion channels which are related structurally to the GABA, glycine and nicotinic acetylcholine receptors. A number of subtypes of 5-HT1 and 5-HT2 receptors have been found, but only a single 5-HT3 receptor unit has so far been detected in mouse, human and guinea pig tissues (Miriq et al. Science (1991) 254:432-437; Belelli et al. Mol Pharmacol (1995) 48:1054-1062; Lankiewicz et al. Mol Pharmacol (1997) 53:202-212). This subunit, designated herein 5-HT3A, has been 25 expressed in oocytes and HEK-293 cells and the recombinantly produced form can mimic many of the properties of the 5-HT3 receptors as they occur in tissues. However, there are sufficient differences that it is suspected that additional 5-HT3 subtypes exist (Bonhaus et al. J Neurochem (1993) 62:1927-1932; Van Hooft et al. J Neurochem (1997) 69:1318-1321; Hussy et al. J Physiol (1994) 418:311-323).
The existence of a multiplicity of subtypes of such receptors is important. Agonists and antagonists can be found that are selective for one subtype or another, thus resulting in different physiological consequences and expanding the repertoire of pharmaceutical substances available for therapy. This enables a more nuanced treatment of various conditions affected by receptor stimulation.
The class of serotonin receptors with which the present invention is concerned, the 5-HT3 class, is evidently involved in the induction of nausea and in behavioral disorders. Apud, Neuropsychopharmacol (1993) 8:117-130. Thus, antagonists of the 5-HT3 receptor would be useful in ameliorating the side-effects of many cancer therapeutic drugs (Gralla et al. New England J Med (1991) 305:905-909). Antagonists to this receptor would also be useful in controlling behavioral disorders (Rodgers et al. Psychopharmacol (1995) 117:306-312; Costall et al. Brit J Pharmacol (1993) 90:89; Zoldan etal. Lancet (1993) 341:562-563).
The present invention provides an additional subtype of the 5-HT3 subclass which thus provides an additional tool for evaluating the selectivity of candidate antagonists and agonists of the serotonin receptor class as well as providing a useful reagent for screening libraries of compounds for desired physiological activities described above.
The invention provides recombinant materials for the production of a previously undescribed subtype of serotonin receptor, designated herein 5-HT3B. The availability of these recombinant materials makes possible high throughput screening of candidate antiemetics and antipsychotic compounds as well as providing a tool for enhancing the selectivity of such compounds in particular individuals and in response to specific conditions.
Thus, in one aspect, the invention is directed to recombinant materials for production of 5-HT3B receptor protein. Two polymorphic forms of the protein have been found associated with a single nucleotide change in the encoding sequence. The amino acid sequences of these forms and set forth in FIGS. 1A and 1B. Also useful are sufficient contiguous fragments of these proteins so as to have substantial functional identity with that of the amino acid sequences of FIG. 1A or 1B when displayed on a cell surface, or proteins with amino acid sequences sufficiently homologous to display the same functional characteristics.
In other aspects, the invention is directed to cells displaying the proteins of FIG. 1A or 1B in a functionally active form and to methods to identify agonists and antagonists of the associated receptor function in assay systems using such cells. The agonists and antagonists identified according to this screen are useful in treating nausea and psychological disorders. The invention is also directed to antibodies that recognize the 5-HT3B receptors, which are useful in purification of this protein, and to oligonucleotide constructs that modulate the production of the receptor in tissues.